Dynamic photoelasticity and dynamic finite element methods were used to study dynamic responses of dynamic tear test (DTT) specimens of a ductile material, that is, 3.2-mm (18-in.) thick polycarbonate sheets. Dynamic photoelastic patterns before and after the onset of unstable fracture showed that the dynamic fracture initiation toughness, KId, was attained during the second maximum load in the hammer load-time history and was approximately 65 percent of the fracture toughness, KIc. Also, dynamic stress intensity factors before and after crack propagation computed by dynamic finite element method using experimentally determined hammer load-time history were in reasonable agreement with those obtained from dynamic photoelasticity. The dynamic finite element analysis also showed that the dynamic fracture initiation toughness could be determined from the dynamic strain response of a strain gage located near the crack tip in conjunction with a simple static analysis.